ABSTRACT
ABSTRACT Magnetically aligned bicelles are an attractive system for structure studies of membrane proteins. They provide a planar liquid crystalline bilayer environment that both immobilizes and aligns the proteins. Bicelles align with the bilayer normal perpendicular to the direction of the magnetic field; therefore, the proteins must undergo rapid rotational diffusion about the normal. We describe a quantitative dynamic model based on the stochastic Liouville equation including uniaxial rotational diffusion. The results show that bicelles modeled as disks undergo rotational diffusion fast enough to average the cylindrical distribution about the bicelle axis. Experimental spectra of a 15N-labeled protein in bicelles are consistent with these calculations. Experimental spectra of mechanically aligned bilayers indicate that the protein itself undergoes rotational diffusion fast enough for the requisite averaging.
